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From:   Parav Pandit <parav@mellanox.com>
To:     Cornelia Huck <cohuck@redhat.com>
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Subject: RE: [PATCH 1/4] mdev: Introduce sha1 based mdev alias
Thread-Topic: [PATCH 1/4] mdev: Introduce sha1 based mdev alias
Thread-Index: AQHVXE6sjQlIhIUUgkClKEYpCVnoRKcOypkAgAAMheCAAAQiAIAAAZ8Q
Date:   Tue, 27 Aug 2019 11:33:54 +0000
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> -----Original Message-----
> From: Cornelia Huck <cohuck@redhat.com>
> Sent: Tuesday, August 27, 2019 4:54 PM
> To: Parav Pandit <parav@mellanox.com>
> Cc: alex.williamson@redhat.com; Jiri Pirko <jiri@mellanox.com>;
> kwankhede@nvidia.com; davem@davemloft.net; kvm@vger.kernel.org; linux-
> kernel@vger.kernel.org; netdev@vger.kernel.org
> Subject: Re: [PATCH 1/4] mdev: Introduce sha1 based mdev alias
>=20
> On Tue, 27 Aug 2019 11:12:23 +0000
> Parav Pandit <parav@mellanox.com> wrote:
>=20
> > > -----Original Message-----
> > > From: Cornelia Huck <cohuck@redhat.com>
> > > Sent: Tuesday, August 27, 2019 3:54 PM
> > > To: Parav Pandit <parav@mellanox.com>
> > > Cc: alex.williamson@redhat.com; Jiri Pirko <jiri@mellanox.com>;
> > > kwankhede@nvidia.com; davem@davemloft.net; kvm@vger.kernel.org;
> > > linux- kernel@vger.kernel.org; netdev@vger.kernel.org
> > > Subject: Re: [PATCH 1/4] mdev: Introduce sha1 based mdev alias
> > >
> > > On Mon, 26 Aug 2019 15:41:16 -0500
> > > Parav Pandit <parav@mellanox.com> wrote:
> > >
> > > > Whenever a parent requests to generate mdev alias, generate a mdev
> > > > alias.
> > > > It is an optional attribute that parent can request to generate
> > > > for each of its child mdev.
> > > > mdev alias is generated using sha1 from the mdev name.
> > >
> > > Maybe add some motivation here as well?
> > >
> > > "Some vendor drivers want an identifier for an mdev device that is
> > > shorter than the uuid, due to length restrictions in the consumers of=
 that
> identifier.
> > >
> > > Add a callback that allows a vendor driver to request an alias of a
> > > specified length to be generated (via sha1) for an mdev device. If
> > > generated, that alias is checked for collisions."
> > >
> > I did described the motivation in the cover letter with example and thi=
s
> design discussion thread.
>=20
> Yes, but adding it to the patch description makes it available in the git=
 history.
>=20
Ok.

> > I will include above summary in v1.
> >
> > > What about:
> > >
> > > * @get_alias_length: optional callback to specify length of the alias=
 to
> create
> > > *                    Returns unsigned integer: length of the alias to=
 be created,
> > > *                                              0 to not create an ali=
as
> > >
> > Ack.
> >
> > > I also think it might be beneficial to add a device parameter here
> > > now (rather than later); that seems to be something that makes sense.
> > >
> > Without showing the use, it shouldn't be added.
>=20
> It just feels like an omission: Why should the vendor driver only be able=
 to
> return one value here, without knowing which device it is for?
> If a driver supports different devices, it may have different requirement=
s for
> them.
>=20
Sure. Lets first have this requirement to add it.
I am against adding this length field itself without an actual vendor use c=
ase, which is adding some complexity in code today.
But it was ok to have length field instead of bool.

Lets not further add "no-requirement futuristic knobs" which hasn't shown i=
ts need yet.
When a vendor driver needs it, there is nothing prevents such addition.

> >
> > > >   * Parent device that support mediated device should be
> > > > registered with
> > > mdev
> > > >   * module with mdev_parent_ops structure.
> > > >   **/
> > > > @@ -92,6 +95,7 @@ struct mdev_parent_ops {
> > > >  	long	(*ioctl)(struct mdev_device *mdev, unsigned int cmd,
> > > >  			 unsigned long arg);
> > > >  	int	(*mmap)(struct mdev_device *mdev, struct vm_area_struct
> > > *vma);
> > > > +	unsigned int (*get_alias_length)(void);
> > > >  };
> > > >
> > > >  /* interface for exporting mdev supported type attributes */
> >